We are in post-war Bosnia, and Kathryn Bolkovac, an experienced cop from Nebraska, has embarked on a tour of duty with contractors for the UN Police Force Monitors, to make big money and get her life back on track. She is divorced, she has a son and a teenage daughter in their father's custody, and police having refused her transfer, she needs the money to be near them.

In Bosnia, she's an anomaly in a mostly male service of ex-soldiers, trying to train a local police force. Her police training and persistence give her an edge: quite early on she's able to advise a local cop on how to help a battered Muslim woman bring assault charges against her husband. The court victory is a first.

It's a sullen, war-devastated landscape, and in its aftermath the UN, and its many subcontractors, have developed a pretty hands-off attitude to local loyalties, resentments and conflicts. This includes the way local men treat their women. One of the fine achievements of this film is its completely convincing evocation of the destruction of community which follows war.

After the small victory in court, Bolkovac is persuaded by a UN Human Rights Commissioner (Vanessa Redgrave) to take on the role of Head of Gender Relations to the UN Mission. A near impossible job, but she brings to it the same no-nonsense attitude she brought to her policing. A pair of quite young girls who have been badly beaten come to her attention. When they are too terrified to name their attackers, she calls a raid on the local bar where they worked. There she finds evidence of many young girls living in appalling conditions, working long shifts as sex workers, and systematically abused. She also discovers that not just the local cops, but a number of UN staffers are regulars at the bar. They may, it seems, be involved not only in the abuse of these woman, but also in their trafficking.

Framed as thriller, The Whistleblower plays out as one, tightly paced and directed. Time and again I was on the edge of my seat, and rigid with outrage at what was being done to these girls and how an entire system was prepared to either participate, collude or turn a blind eye.As Bolcovak, Rachel Weisz is very good indeed. It's such a disciplined performance that we are to overlook what the camera cannot hide -- her remarkable beauty -- to focus on the emotions within, and the battle she fights.

The Whistleblower is a first feature from Canadian writer Larysa Kondraki. It is indeed based on the experiences of the real Kathryn Bolkovac, who ended her time in Bosnia suing the UN Contractors DYNCORP for unfair dismissal.

Kondraki, of Ukrainian descent, read about the epidemic of sex trafficking in Eastern Europe, sought out Bolkovac and, with co-writer Eilas Kirwan spent two years in Eastern Europe researching the film.

Its a fine achievement, cinematically, dramatically and also ethically. Kondraki does not go for easy sentiment. It's told from Bolkavac's POV, a woman driven to act on behalf of young girls who are under such duress, unable to speak for themselves. The issues of trust and responsibility, and cross-cultural limitations, are keenly felt. It's all the the more convincing for this restraint. Highly recommended.